In many communication systems, data packages are transmitted sequentially. The hop timing (i.e. the time delta between two packages) is usually fixed. Some systems use the same carrier frequency for transmitting all data packages and some systems employ frequency hopping, where the frequency used for transmitting one package, the frequency used for transmitting the immediately preceding package and the frequency used for transmitting the immediately following package are different. FIG. 1A is a diagram illustrating a transmission scheme. This scheme may be implemented by systems such as Ultra-Wideband (UWB) systems developed based on Multi-Band Orthogonal Frequency Division Multiplexing Alliance's (MBOA) 802.15.3a standard. Transmission of the data symbols is shown along the time axis and the frequency axis. In this example, symbols 100, 102 and 104 occupy substantially non-overlapping frequency bands Fa, Fb and Fc respectively. In FIG. 1A, data symbols transmitted at different frequencies are shown to be transmitted in their respective time slots. The transmission frequency pattern is then repeated.
FIG. 1B is another diagram illustrating the transmission scheme shown in FIG. 1A. For the purpose of illustration, transmission of the data packages is shown along the time axis while the frequency axis is omitted. Time slots such as 100, 102 and 104 are represented using blocks with frequency labels Fa, Fb and Fc, respectively. In the example shown, all the time slots are in use and data symbols are transmitted at full symbol rate.
Sometimes it may be useful to transmit the data symbols at a lower rate so that parts of the transmitter may be turned off or disabled when no data is transmitted in order to conserve power. FIG. 1C is a diagram illustrating a half rate transmission scheme. In the diagram shown, data packages are transmitted during every other time slot. FIG. 1D is a diagram illustrating a transmission scheme in which data is transmitted at one third of the full rate. In this scheme, data packages are transmitted during one out of three consecutive time slots and the rest of the time slots are inactive. The proposed schemes such as the ones shown in FIGS. 1C and 1D typically requires the radio to be turned on and off very rapidly. For example, in the MBOA 802.15.3a standard, each time slots is 312.5 nanoseconds in length. Because the radio can stay off for only one or two time slots, and because the radio components commonly require longer settling time, it is often challenging to implement a transmitter that can switch on and off within the allotted time. It would be desirable to have a way to allow reduced transmission rate and receive the benefits associated with a lower transmission rate, without imposing further limitations on the transmitter design.